Exercise Contents:
Return to Module 10

Atlantic Forest

Exercise 10: Soils, Land Use, and Biodiversity
Module 10: Geology and Soils

By T. Kittel

Your Questions

  1. What are the processes that lead to the development of soils?
  2. Why are soils different from one location to another (locally and globally) and how does vertical structure in a soil profile develop?
  3. How do we describe a soil and its profile? What are the appropriate terms to use for this activity?

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Background

The purpose of this exercise is to cover concepts and techniques related to soils. The exercise covers two related areas. The first is conceptual: What are the processes that lead to the development of soils? – why are soils different from one location to another (locally and globally) and how does vertical structure in a soil profile develop? The second area is soil description – use of terms and techniques to describe a soil and it profile. The exercise starts off by creating a soil description for one or two sites in the class’s biome and discussion of the processes at play that have led to development of these soils. This was, in the context of previous years, a “shared exercise,” so the exercise finishes up by addressing the question: How do soils found in other biomes differ from those described by the class from the local biome? Background material.

1) Discussion of Jenny’s five Factors of Soil Formation controlling the development of soils – soil parent material, regional climate, local topography (aspect, drainage), organisms (vegetation, soil fauna), and time (as in Module 10 write-up, order whatever works). Key is that the factors are independent, that’s why it’s ‘regional’ climate, as opposed to climate modified by topography or vegetation. This conceptual framework will be familiar if Major’s five functional factors for plant ecology (developed from Jenny’s book – Jack Major was one of Hans Jenny’s students) was presented in earlier exercises related to understanding vegetation/biome distribution.

2) Introduce (or restate) the concept that soil is a world of life (bacteria, fungi, nematodes, insects, larger organisms) vs. simply a substrate for plants – this should link back to the decomposition module (Ex 8).

3) Description of soil profiles – define general terms for defining soil horizons and soil characteristics.

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Your Assignment

A. Beforehand: Are soil pits allowed at the site? And if so how physically difficult is it to dig a pit in the site’s soils?

B. Field work. The class digs a soil pit at least at two different environments to compare and contrast sites with different vegetation, parent material, drainage, or age. Possibly a core forest site and a more recent depositional zone where soil is poorly developed would be appropriate. For each soil pit, the students should collect the following information:

  1. Site variables - latitude, longitude, elevation, vegetation, landform (terrace, flood plain, hillslope) and landscape position (with respect to drainage, exposure, etc), slope,
  2. Identify and visually describe soil profile horizons – use characteristics such as organic matter, color, structure (e.g., prismatic), consistence (e.g., friable), etc., per handouts Take photos of profile.
  3. For each layer, take a sample for lab work

C. In the lab, record following soil characteristics:

  1. Color – using Munsell soil color book. Use both dry and wet smudge tests (take photos).
  2. Texture – put aside some of each layer’s sample for use in (b), before doing (a).
  3. a. Using soil sieves. The instruction sheet with the sieves gives the grain sizes collected by each level, and how to interpret. The last screen gives “silt+clay”
  4. b. Ball, ribbon (plasticity), and stickiness tests on non-detritus and non-rock fraction – put a fresh subample [that is, not the portion used in (a)] through screen #60 first to do this test.
  5. Calcium carbonate (effervescence) test – using HCl if available

D. Write-ups. Create a soil site description for soils evaluated. Address the questions:

  1. What processes determined the characteristics observed? (how did the soil form? – e.g. under current or different conditions? – similar climate or a paleoclimate, under different erosional/deposition environment/landscape position, etc.)
  2. How would you expect that soils might vary across the landscape at the site?
  3. Describe and explain differences between this site’s soils and those at other SEE-U sites.

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Procedural Notes

The following websites will be very helpful for conducting this exercise:
  1. A general overview to soil science and why it is important
  2. Finding and describing soil horizons
  3. An illustration of the soil textural triangle
  4. Soil texture by feel guide

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Materials Needed

  1. Methods handouts on soil description techniques.
  2. Field: Shovel (preferably a narrow bladed “sharpshooter” soil pit shovel), measuring tape, large nails with colored surveying tape to mark layers, digital camera, GPS, compass (for local aspect, slope), plastic sample bags, marker pens, field notebook, work gloves.
  3. Lab: materials required for soil description techniques as per handouts. Including: soil sieves, HCl solution, Munsell soil color book (and non-color blind observers), soil texture triangle (for soil texture classes).
  4. For local site write-up: Local geology and soils maps if available, soil pit info from last year for comparison. Also web site url for giving example of soil site descriptions. (last year, Erika pointed the students to a U Arizona site at, however, that URL isn't working now. Other possibilities might be Natural Resource Conservation Service site.
  5. For interbiome comparisons: Student presentations for Ex 10 from Black Rock in 2000 and the different sites at B2 for 2001. See above for these links.

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All Materials Copyright © 2002 by T. Kittel.
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